Vented plug assemblies for wellbores

ABSTRACT

Plug assemblies such as sealing devices comprise a vent tube disposed above the sealing device. The vent tube is selectively place in, and out of, fluid communication with a lower zone of a wellbore so that during curing of cement or other sealing material disposed on top of the sealing device, gas is permitted to flow from the lower zone to the surface of the wellbore. As a result, the likelihood of gas corrupting or otherwise leaking around the interface of the sealing element with the wall of the wellbore is decreased. After the cement has cured, fluid communication between the vent pipe and the lower zone is closed to isolate the lower zone from the upper zone disposed above the sealing device.

BACKGROUND

1. Field of Invention

The invention is directed to plug assemblies for use in oil and gaswells and, in particular, a plug assemblies comprising a vent tube forventing during curing of cement or resin disposed on top of the plugassemblies.

2. Description of Art

Plug assemblies comprising sealing devices such as packers and bridgeplugs for sealing wellbores are known in the art. For example, somesealing devices include an expandable sealing element such as a rubbercasing or bladder or balloon that is inflated by fluid pumped down atubing string. In certain of these sealing devices the rubber casing orbladder or balloon include swellable materials encased within anexpandable sealing element such as a rubber casing or balloon are knownin the art. These types of sealing devices expand and, thus, seal to theinner wall surface of a wellbore by contacting hydraulic fluid or otherfluid with the swellable materials encased within the rubber casing sothat the swellable materials absorb the fluid and expand. In one type ofthese sealing devices, for example, hydraulic fluid is pumped down astring of tubing having the sealing device secured thereto. Thehydraulic fluid travels down the bore of the string of tubing andthrough a port that is in fluid communication with an inner cavity ofthe rubber casing. Swellable materials disposed within the rubber casingare contacted by the hydraulic fluid. As a result, the swellablematerials absorb the fluid and expand. As the swellable materials expandand hydraulic fluid is pumped into the rubber casing, the rubber casingexpands to seal the wellbore. After expansion, hydraulic fluid pressureis decreased and the rubber casing remains is held in the expandedposition solely by the swellable materials having absorbed the fluid.

Regardless of how the sealing device is deployed in the wellbore, incertain applications the sealing device is secured in place to form a“permanent” plug of the wellbore by disposing a sealing material such ascement, resin, or other material on top of the sealing device. Thesealing material is used in an attempt to stop gas percolation in thewellbore. Gas percolation occurs when a gas disposed below the sealingdevice “leaks” or migrates around the sealing element, such as throughirregularities in the casing of the wellbore to which the sealing deviceis contacted. Although the sealing material is placed on top of thesealing device to prevent the gas from traveling to the surface of thewell, sometimes, the gas creates a path through the uncured sealingmaterial causing a leak path to be formed and, therefore, underminingthe effectiveness of the sealing device to completely isolate the zoneof the wellbore disposed below the sealing device.

SUMMARY OF INVENTION

Broadly, the sealing devices disclosed herein include a vent tubedisposed above the sealing device to keep cement, resin, or othersealing material from being compromised by gas percolation during curingof the cement, resin, or other sealing material. The vent tube comprisesa bore that is in fluid communication with the bore of a sealing device,the bore of an on-off connector and the bore of a tubing stringconnected to the on-off connector. In one embodiment, the sealing deviceincludes valve such as a removable plug so that the bore of the sealingdevice can be selectively opened and closed to flow through the sealingdevice to the portion of the wellbore disposed below the sealing device,i.e., the lower zone. The removable plug is initially disposed in thesealing device, or the valve is initially in its closed position, sothat there is no fluid communication through the sealing device to thelower zone. As a result, fluid within the bores of the tubing stringactuates the sealing device so that the sealing element of the sealingdevice engages the wall of the wellbore to isolate the wellbore intoupper and lower zones. The upper zone is the portion of the wellboredisposed above the sealing device and, as mentioned above, the “lowerzone” is the portion of the wellbore disposed below the sealing device.

In one particular embodiment, a lower sub comprising the valve, e.g.,removable plug is attached to the lower end of the sealing device.

In operation, the sealing device is secured to a tool string thatcomprises a vent tube releasably secured to the upper end of the sealingdevice, an on-off connector releasably secured to the upper end of thevent tube, and tubing releasably secured to the upper end of the on-offconnector. In one particular embodiment, a lower sub is releasablysecured to the lower end of the sealing device. The tool string is thenrun to depth in the wellbore and the sealing device is actuated, e.g.,inflated or expanded such as through application of fluid pressure andpressure, to set the sealing device within the wellbore. Afteractuation, fluid communication between the bore of the sealing deviceand the lower zone is established such as by opening a valve in thesealing device or in the lower sub, or removing a plug previouslydisposed within the bore of the sealing device or the lower sub. Aftersuch fluid communication is established, a flow path is created betweenthe lower zone and the surface of the wellbore. Thus, the vent tubepermits gas to “vent” or flow from the lower zone to the upper zone and,thus, to the surface of the wellbore.

Thereafter, cement, resin, or other sealing material is disposed on topof the sealing device and around the vent tube such as by using a smallstring of pipe pumping the sealing material around an annulus formed bythe vent tube and the wellbore wall. The sealing material is permittedto cure. During this time period, gas is permitted to flow from thelower zone to the upper zone through the tubing. Because of the fluidcommunication between the lower zone through the vent tube, theprobability of gas migrating around the sealing element of the sealingdevice is lessened because the gas is permitted to flow through the venttube instead of having to force its way around the sealing element.After the sealing material has cured, the removable plug is reinstalled,or the valve closed and the on-off connector is actuated to release thetool string from the vent tube leaving a permanent installation thatisolates the lower zone from the upper zone.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a partial cross sectional view of wellbore comprising onespecific embodiment of the sealing device with vent tube disclosedherein.

While the invention will be described in connection with the preferredembodiments, it will be understood that it is not intended to limit theinvention to that embodiment. On the contrary, it is intended to coverall alternatives, modifications, and equivalents, as may be includedwithin the spirit and scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF INVENTION

Referring now to FIG. 1, one specific embodiment of sealing device 60 isdescribed broadly with respect to wellbore 10 disposed within formation12 having casing string or casing 14 disposed therein. Sealing device 60is secured to tool string 100 and run-in and set (as shown in FIG. 1).Broadly, tool string 100 comprises lower sub 30, vent tube 40, andon-off connector 50, and sealing device 60.

Lower sub 30 comprises upper and lower ends, bore 32, and removable plug34. Upper end is releasably secured to the lower end of sealing device60 so that bore 32 is in fluid communication with bore 62 of sealingdevice 60 (discussed in greater detail below).

Vent tube 40 comprises one or more joints of tubing releasably securedto the upper end of sealing device 60. Vent tube 40 comprises vent tubebore 42 in fluid communication with sealing device bore 62 and bore 52of on-off connector 50.

In the embodiment of FIG. 1, sealing device 60 is an inflatable-typesealing device comprising a bore 62 in fluid communication with aninterior area (not shown) of sealing element 64. In operation of settingsealing device 60, tool string 100 is assembled and run to depth withinwellbore 10. Fluid (not shown) is pumped down a bore of tool string 100,through bore 52 of on-off connector, through bore 42 of vent tube 40,into bore 62 of sealing device and into bore 32 of lower sub 30. Duringrun-in and actuation of sealing device 60, removable plug 34 is disposedwithin bore 32 of lower sub 30 so that fluid pumped down the bore oftool string 100 flows from bore 32 into the interior area of the sealingelement 34 to inflate and set sealing device 30 within wellbore 10. Inother words, removable plug 34 prevents fluid flowing down tool string100 during actuation of sealing device 60 from flowing out of the lowerend of lower sub into lower zone 18 of wellbore 10. Actuation of sealingdevice 60 isolates the portion of wellbore 10 disposed below sealingdevice 60, referred to herein as lower zone 18 from the portion ofwellbore 10 disposed above sealing device 60, referred to herein asupper zone 20.

After sealing device 60 is actuated to its set position, fluid pressureis “backed-off” or reduced and removable plug 34 is removed from bore 32of lower sub 30 (as shown in FIG. 2) such as by running a tubing string(not shown) down through the bore of tool string 100, through on-offconnector bore 52, vent tube bore 42, sealing device bore 62, and intolower sub bore 32. Thus, as shown in FIG. 2, fluid communication isestablished between lower zone 18 and the surface of wellbore 10.

After removable plug 34 is removed, cement, resin, or other sealingmaterial 24 (FIG. 2) is disposed on top of sealing device 60 withinannulus 22 (shown in FIG. 1) defined by the space between the outer wallsurface of vent tube 40 and inner wall surface 15 of casing 14. Theamount of sealing material disposed on top of sealing device 60 can bemodified as desired by the operator, provided however, that the amountof sealing material does not rise so high that on-off connector 50cannot operate. Thereafter, the sealing material is permitted to curethrough any method known in the art. During the curing step, gasdisposed in lower zone 18 is permitted to flow through bore 32, sealingdevice bore 62, vent tube bore 42, on-off connector bore 52, and throughthe bore of tool string 100 to the surface of wellbore 10 (FIG. 2).

Referring now to FIG. 3, after the sealing material has cured, removableplug 34 is reinstalled within bore 32 such as by running a tubing string(not shown) down through the bore of tool string 100, through on-offconnector bore 52, vent tube bore 42, sealing device bore 62, and intolower sub bore 32. Thereafter, on-off connector 50 is actuated todisconnect from vent tube 40 leaving sealing device 60 secured in placewithin wellbore 10 such that upper zone 20 is isolated from lower zone18 as shown in FIG. 3.

It is to be understood that the invention is not limited to the exactdetails of construction, operation, exact materials, or embodimentsshown and described, as modifications and equivalents will be apparentto one skilled in the art. For example, a removable plug may be a valvethat can be actuated from the surface of the wellbore. Additionally, thesealing device may include the valve, e.g., removable plug, such thatlower sub is not needed. Further, on-off connector may be any deviceknown in the art that is capable of releasing the connection between theon-off connector and the vent tube. Moreover, the sealing device is notrequired to be an inflatable-type sealing device. Instead, it can be a“swellable-type” sealing device or any other type of sealing deviceknown in the art. Accordingly, the invention is therefore to be limitedonly by the scope of the appended claims.

1. A plug assembly for installation into a wellbore, the plug assembly comprising: a sealing device comprising a sealing element, sealing device bore, the bore being in fluid communication with the sealing element at a first location and the bore being in fluid communication with a valve at a second location, wherein the first location is disposed above the second location; a vent tube comprising a vent tube bore in fluid communication with the sealing device bore, the vent tube being disposed above the sealing device; and a release assembly comprising a release assembly bore in fluid communication with the vent tube bore, the release assembly being releasably connected to the vent tube.
 2. The plug assembly of claim 1, wherein the valve is disposed within a lower sub-assembly disposed below the sealing device, the lower sub-assembly comprising a lower sub-assembly bore, the valve being disposed within the lower sub-assembly bore.
 3. The plug assembly of claim 2, wherein the valve comprises a removable plug.
 4. The plug assembly of claim 1, wherein the vent tube comprises two or more joints of tubing.
 5. The plug assembly of claim 1, wherein the sealing element comprises at least one swellable material.
 6. The plug assembly of claim 1, wherein the sealing element comprises an inflatable bladder.
 7. A method of installing a plug to a wellbore, the method comprising the steps of: (a) assembling a tubing string comprising a release assembly comprising a release assembly bore, the release assembly being releasably connected to a vent tube comprising a vent tube bore, the vent tube being connected to a sealing device comprising a sealing device bore, the release assembly being disposed above the vent tube and the vent tube being disposed above the sealing device, the release assembly bore, vent tube bore, and sealing device bore each being in fluid communication with each other and in fluid communication with a valve; (b) running the tubing string into a wellbore to a desired location; (c) disposing the valve in a closed position; (d) pumping fluid down the tubing string to actuate the sealing device causing a sealing element of the sealing device to engage an inner wall surface of the wellbore; (e) disposing the valve in an opened position; (f) disposing a sealing material on top of the sealing device in an annulus formed by an outer wall surface of the vent tube and the inner wall surface of the wellbore; (g) allowing the sealing material to cure; (h) disposing the valve in the closed position; and (i) actuating the release assembly to disconnect the tubing string from the vent tube and remove the tubing string from the wellbore.
 8. The method of claim 7, wherein the valve comprises a removable plug and step (e) is performed by running a tool string down the bores of the release assembly, vent tube, and sealing device to engage the removable plug and retracting the tool string from the bores of the release assembly, vent tube, and sealing device.
 9. The method of claim 8, wherein step (h) is performed by running a tool string down the bores of the release assembly, vent tube, and sealing device to dispose the removable plug in the sealing device bore and retracting the tool string from the bores of the release assembly, vent tube, and sealing device. 